[PATCH] VT locking fixes

From: Benjamin Herrenschmidt <benh@kernel.crashing.org>

- Make sure that all console operations are approriately protected under
  console_sem.

- Adds checks to make sure that people are taking console_sem when it is
  expected to be held.

drivers/char/selection.c

@@ -24,6 +24,7 @@
 #include <linux/consolemap.h>
 #include <linux/selection.h>
 #include <linux/tiocl.h>
+#include <linux/console.h>
 
 #ifndef MIN
 #define MIN(a,b)	((a) < (b) ? (a) : (b))
@@ -290,7 +291,10 @@ int paste_selection(struct tty_struct *tty)
 	int	pasted = 0, count;
 	DECLARE_WAITQUEUE(wait, current);
 
+	acquire_console_sem();
 	poke_blanked_console();
+	release_console_sem();
+
 	add_wait_queue(&vt->paste_wait, &wait);
 	while (sel_buffer && sel_buffer_lth > pasted) {
 		set_current_state(TASK_INTERRUPTIBLE);

drivers/char/tty_io.c

@@ -1484,7 +1484,12 @@ static int tiocswinsz(struct tty_struct *tty, struct tty_struct *real_tty,
 #ifdef CONFIG_VT
 	if (tty->driver->type == TTY_DRIVER_TYPE_CONSOLE) {
 		unsigned int currcons = tty->index;
-		if (vc_resize(currcons, tmp_ws.ws_col, tmp_ws.ws_row))
+		int rc;
+
+		acquire_console_sem();
+		rc = vc_resize(currcons, tmp_ws.ws_col, tmp_ws.ws_row);
+		release_console_sem();
+		if (rc)
 			return -ENXIO;
 	}
 #endif

drivers/char/vt_ioctl.c

@@ -470,6 +470,9 @@ int vt_ioctl(struct tty_struct *tty, struct file * file,
 		 * currently, setting the mode from KD_TEXT to KD_GRAPHICS
 		 * doesn't do a whole lot. i'm not sure if it should do any
 		 * restoration of modes or what...
+		 *
+		 * XXX It should at least call into the driver, fbdev's definitely
+		 * need to restore their engine state. --BenH
 		 */
 		if (!perm)
 			return -EPERM;
@@ -492,10 +495,12 @@ int vt_ioctl(struct tty_struct *tty, struct file * file,
 		/*
 		 * explicitly blank/unblank the screen if switching modes
 		 */
+		acquire_console_sem();
 		if (arg == KD_TEXT)
 			unblank_screen();
 		else
 			do_blank_screen(1);
+		release_console_sem();
 		return 0;
 
 	case KDGETMODE:
@@ -665,18 +670,29 @@ int vt_ioctl(struct tty_struct *tty, struct file * file,
 			return -EFAULT;
 		if (tmp.mode != VT_AUTO && tmp.mode != VT_PROCESS)
 			return -EINVAL;
+		acquire_console_sem();
 		vt_cons[console]->vt_mode = tmp;
 		/* the frsig is ignored, so we set it to 0 */
 		vt_cons[console]->vt_mode.frsig = 0;
 		vt_cons[console]->vt_pid = current->pid;
 		/* no switch is required -- saw@shade.msu.ru */
 		vt_cons[console]->vt_newvt = -1; 
+		release_console_sem();
 		return 0;
 	}
 
 	case VT_GETMODE:
-		return copy_to_user((void*)arg, &(vt_cons[console]->vt_mode), 
-							sizeof(struct vt_mode)) ? -EFAULT : 0; 
+	{
+		struct vt_mode tmp;
+		int rc;
+
+		acquire_console_sem();
+		memcpy(&tmp, &vt_cons[console]->vt_mode, sizeof(struct vt_mode));
+		release_console_sem();
+
+		rc = copy_to_user((void*)arg, &tmp, sizeof(struct vt_mode));
+		return rc ? -EFAULT : 0;
+	}
 
 	/*
 	 * Returns global vt state. Note that VT 0 is always open, since
@@ -718,7 +734,9 @@ int vt_ioctl(struct tty_struct *tty, struct file * file,
 		if (arg == 0 || arg > MAX_NR_CONSOLES)
 			return -ENXIO;
 		arg--;
+		acquire_console_sem();
 		i = vc_allocate(arg);
+		release_console_sem();
 		if (i)
 			return i;
 		set_console(arg);
@@ -768,17 +786,20 @@ int vt_ioctl(struct tty_struct *tty, struct file * file,
 				 * The current vt has been released, so
 				 * complete the switch.
 				 */
-				int newvt = vt_cons[console]->vt_newvt;
+				int newvt;
+				acquire_console_sem();
+				newvt = vt_cons[console]->vt_newvt;
 				vt_cons[console]->vt_newvt = -1;
 				i = vc_allocate(newvt);
-				if (i)
+				if (i) {
+					release_console_sem();
 					return i;
+				}
 				/*
 				 * When we actually do the console switch,
 				 * make sure we are atomic with respect to
 				 * other console switches..
 				 */
-				acquire_console_sem();
 				complete_change_console(newvt);
 				release_console_sem();
 			}
@@ -806,16 +827,21 @@ int vt_ioctl(struct tty_struct *tty, struct file * file,
 			return -ENXIO;
 		if (arg == 0) {
 		    /* disallocate all unused consoles, but leave 0 */
+			acquire_console_sem();
 			for (i=1; i<MAX_NR_CONSOLES; i++)
 				if (! VT_BUSY(i))
 					vc_disallocate(i);
+			release_console_sem();
 		} else {
 			/* disallocate a single console, if possible */
 			arg--;
 			if (VT_BUSY(arg))
 				return -EBUSY;
-		    if (arg)			      /* leave 0 */
+			if (arg) {			      /* leave 0 */
+				acquire_console_sem();
 				vc_disallocate(arg);
+				release_console_sem();
+			}
 		}
 		return 0;
 
@@ -828,8 +854,11 @@ int vt_ioctl(struct tty_struct *tty, struct file * file,
 		if (get_user(ll, &vtsizes->v_rows) ||
 		    get_user(cc, &vtsizes->v_cols))
 			return -EFAULT;
-		for (i = 0; i < MAX_NR_CONSOLES; i++)
+		for (i = 0; i < MAX_NR_CONSOLES; i++) {
+			acquire_console_sem();
                         vc_resize(i, cc, ll);
+			release_console_sem();
+		}
 		return 0;
 	}
 
@@ -870,11 +899,13 @@ int vt_ioctl(struct tty_struct *tty, struct file * file,
 		for (i = 0; i < MAX_NR_CONSOLES; i++) {
 			if (!vc_cons[i].d)
 				continue;
+			acquire_console_sem();
 			if (vlin)
 				vc_cons[i].d->vc_scan_lines = vlin;
 			if (clin)
 				vc_cons[i].d->vc_font.height = clin;
 			vc_resize(i, cc, ll);
+			release_console_sem();
 		}
   		return 0;
 	}

include/linux/console.h

@@ -102,6 +102,14 @@ extern void acquire_console_sem(void);
 extern void release_console_sem(void);
 extern void console_conditional_schedule(void);
 extern void console_unblank(void);
+extern int is_console_locked(void);
+
+/* Some debug stub to catch some of the obvious races in the VT code */
+#if 1
+#define WARN_CONSOLE_UNLOCKED()	WARN_ON(!is_console_locked() && !oops_in_progress)
+#else
+#define WARN_CONSOLE_UNLOCKED()
+#endif
 
 /* VESA Blanking Levels */
 #define VESA_NO_BLANKING        0

kernel/power/console.c

@@ -6,6 +6,7 @@
 
 #include <linux/vt_kern.h>
 #include <linux/kbd_kern.h>
+#include <linux/console.h>
 #include "power.h"
 
 static int new_loglevel = 10;
@@ -18,14 +19,20 @@ int pm_prepare_console(void)
 	console_loglevel = new_loglevel;
 
 #ifdef SUSPEND_CONSOLE
+	acquire_console_sem();
+
 	orig_fgconsole = fg_console;
 
-	if (vc_allocate(SUSPEND_CONSOLE))
+	if (vc_allocate(SUSPEND_CONSOLE)) {
 	  /* we can't have a free VC for now. Too bad,
 	   * we don't want to mess the screen for now. */
+		release_console_sem();
 		return 1;
+	}
 
 	set_console(SUSPEND_CONSOLE);
+	release_console_sem();
+
 	if (vt_waitactive(SUSPEND_CONSOLE)) {
 		pr_debug("Suspend: Can't switch VCs.");
 		return 1;
@@ -40,12 +47,9 @@ void pm_restore_console(void)
 {
 	console_loglevel = orig_loglevel;
 #ifdef SUSPEND_CONSOLE
+	acquire_console_sem();
 	set_console(orig_fgconsole);
-
-	/* FIXME: 
-	 * This following part is left over from swsusp. Is it really needed?
-	 */
-	update_screen(fg_console);
+	release_console_sem();
 #endif
 	return;
 }

kernel/printk.c

@@ -62,6 +62,15 @@ int oops_in_progress;
  */
 static DECLARE_MUTEX(console_sem);
 struct console *console_drivers;
+/*
+ * This is used for debugging the mess that is the VT code by
+ * keeping track if we have the console semaphore held. It's
+ * definitely not the perfect debug tool (we don't know if _WE_
+ * hold it are racing, but it helps tracking those weird code
+ * path in the console code where we end up in places I want
+ * locked without the console sempahore held
+ */
+static int console_locked;
 
 /*
  * logbuf_lock protects log_buf, log_start, log_end, con_start and logged_chars
@@ -524,6 +533,7 @@ asmlinkage int printk(const char *fmt, ...)
 		goto out;
 	}
 	if (!down_trylock(&console_sem)) {
+		console_locked = 1;
 		/*
 		 * We own the drivers.  We can drop the spinlock and let
 		 * release_console_sem() print the text
@@ -557,10 +567,17 @@ void acquire_console_sem(void)
 	if (in_interrupt())
 		BUG();
 	down(&console_sem);
+	console_locked = 1;
 	console_may_schedule = 1;
 }
 EXPORT_SYMBOL(acquire_console_sem);
 
+int is_console_locked(void)
+{
+	return console_locked;
+}
+EXPORT_SYMBOL(is_console_locked);
+
 /**
  * release_console_sem - unlock the console system
  *
@@ -592,12 +609,14 @@ void release_console_sem(void)
 		spin_unlock_irqrestore(&logbuf_lock, flags);
 		call_console_drivers(_con_start, _log_end);
 	}
+	console_locked = 0;
 	console_may_schedule = 0;
 	up(&console_sem);
 	spin_unlock_irqrestore(&logbuf_lock, flags);
 	if (wake_klogd && !oops_in_progress && waitqueue_active(&log_wait))
 		wake_up_interruptible(&log_wait);
 }
+EXPORT_SYMBOL(release_console_sem);
 
 /** console_conditional_schedule - yield the CPU if required
  *
@@ -633,6 +652,7 @@ void console_unblank(void)
 	 */
 	if (down_trylock(&console_sem) != 0)
 		return;
+	console_locked = 1;
 	console_may_schedule = 0;
 	for (c = console_drivers; c != NULL; c = c->next)
 		if ((c->flags & CON_ENABLED) && c->unblank)